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Chapter 13

PSYB65 chapter 13.docx

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Ted Petit

Chapter 13 Early development - Neural plate: patch of cells that are on dorsal surface of the embryo which eventually becomes the nervous system o It forms from the ectoderm of embryo o Cells here are stem cells that are pluripotent – potential to develop into different types of nervous system cells - Forms groove, forms neural tube, which starts to form ventricles and central canal of spinal cord - During proliferation, ventricular zone rapidly divide and by day 40 there are 3 prominent bumps on the anterior portion of the neural tube – forebrain, midbrain, hindbrain - Cells also migrate from interior ventricular zone by following glia - Waves of proliferation and migration develop CNS - Deeps layer of neurons develop first and migrate inside out - After migration they grow axon and dendrites - Cell differentiation complete at birth - Axons and dendrites must grow toward targets. How they do is unknown. - Brain particularly vulnerable during last 4-5 months of gestation but failures can happen any time. Can be external or genetic or chromosomal - Failure for neural tube to close- craniorachischisis (sadly this is not a typo!!)- groove in top of head and body. Syndromes range from spina bifidia to anencephaly from partial closure. - Anenephaly occurs when rostral part of neural plate doesn’t fuse. Absence of cerebral hemispheres. Generally fatal. - Spina bifida caused by failure of neural tube to close completely. Neurological difficulties with locomotion. Primary effects on spinal cord. Later can result in other abnormalities - By 7 months most neurons have migrated and differentiated into final forms - Neurons undergo synaptogenesis and dendritic branching producing far more synapses and dendrites than needed which occur after birth and into adulthood. Occurs gradually. Most of it happens without experience but at birth to 2 years, it goes through rapid growth. After that comes synapse reduction - Synapse reduction reaches maximum at puberty - About 50% more neurons are produced in developing brain than is required. Death is normal and critical feature in development. Neural death is apoptotic or planned – this controlled by genes - Apoptotic changes and synaptic pruning occurs after birth and may be very dependent on environment and experience Postnatal Development - Cortex grows 4x bigger from brith to adulthood - There are different possible approaches to study relation between cortical growth and behavioural change o Eg. See if behaviours are evident only when brain reaches certain elvel of maturation o Whether or not emergence of specific behaviours is associated with development of specific aspects of motor cortex - Plastic change- ability of CNS to alter itself in response to environmental stimuli - Crtical periods of plastic change- environment can have maximal effect on CNS o Longer lived species exhibit prolonged critical periods that occur later in life well beyond prenatal period o Experience expectant: CNS changes dependent on experiences during critical period for specific synapses develop as they should  Eg. Sensory cortex o Experience-dependent: idiosyncratic experiences that occur during critical periods that also affect brain development  Eg. Musical training can have long-lasting changes on size of auditory cortex. Most prominent in those who practed at 9 years old. Same with motor cortex who played stringed instruments - Cortical gray matter increase until 4- from postnatal growth, plastic change from synaptogenesis, myelination, dendritic branching - Synapotenesis and dendritic branching occur prenatally and postanatally and aer presumably maximal during critical periods - Neurotrophins(chemicals secreted by brain that enhances survival of nerons) and neutrotransmitters – has to do with nerve growth and change in response to environmental events - Both synapotenesis and dendritic branching sensitive to experience-expectant/dependent plasticity - White matter grows steadily until 20 years of age - Much of cortex isn’t myelinated, whereas primary motor and sensory area is completely myelinated by 4 - Myelination corresponds to emergence of behavior o So sensory and motor behavior emerges first because its completed mytelination. Complex behaviours however emerge later. o Not causal relationship Parietal lobe - Inconsistent development. Some parts fully functional t birth (eg. Reflexes) but other parts take longer. - 2-3 months babies exhibit large increases in glucose utilization in parietal lobes until 2-3 years old. Coreresponds to improvements in visuospatial and visuosensorimotor skill. - Preschool children have trouble with tactile discrimination (eg. Localizing point on their hands) - Also deals with dorsal visual strea, processing spatial information and directing behavior. Processes motion. o 7 weeks prefer moving to stationary objects. First sensitive to motion at 12 week. Global motion appears at age 4 - Williams syndrome – chromosome deleted. mild to moderate cognitive impairments. Lower brain volume, but is inconsistent. Most reduction in parietal and occipital lobe. Impairments in visuospatial ability. Thus chromosome 7 underly typical development of parietal, occipital and/or white matter in CNS Occipital lobe - Newborns have pretty good visual systems. Can distinguish 2D and 3D. competence depends on myelination of optic tract and optic radiation which by 3 months are heavily myelinated. - Behaviourally, many visual behaviors change rapidly following birth. At 6 weeks, infants begin to experience binocular vision and is stable by 6 months of age - Development is critically dependent on environmental experience. Eg. Congenital cataracts uncorrected leads to irreversible changes to visual cortex o If removed after critical period, normal eye has poor visual acuity – amblyopia and limited or no binocular vision o When eyes are misaligned in strabismus, impaired depth perception if correction is after critical period - Critical period for binocular vision = first few months of life and peaks 1-3 years of age. So when strabismus develops after age 4, no long lasting effects - Some visual functions that are more complex may nto develop until teens. Eg. Ability to match emotional faces with cues in cartoon develops at age 14 Temporal lobe development - 2 main types: linguistic and hippocampally de3pendent memory function - Language requires temporal and frontal lobes and myelination of connections among the lobes - Auditory cortex functional at birth but doesn’t make functional connections for language - Wenicke’s area and broca’s area undergo dendritic branching and synaptic remodeling during second year of life. Other commissural systems are undergoing myelination at ages 1-2 too - Left temporal and frontal lobes connect increasing functional connectivity both ipsilaterally and bilaterally. Failure to experience linguistic stimulation at this time will result in permanent deficits in linguistic skill (thus critical period is before 2) - From 2-12 years, dendrite arborizations occur in speech areas in brain. Other areas are sensitive to environmental factors, suggesting means for the environment to affect language development - Neural maturation and linguistic ability have large environmental component - Hippocampus is adult volume at 7-10 months. Hippocampus shows high levels of glucose utilization from birth. But many hippocamplly dependent memory processes not mature at birth. - Hippocampus exhibits neurogenesis. Memory functions of the hippocampus result from its ability to extend its developmental period throughout the lifespan - Memory functions of hippocampus rely on functional connections with parietal and frontal lobes and many hipocampally dependent memory functions develop over course of first 5-7 years o Eg. Visual memory not adult leve until 5 o Autobiographical or episodic information doesn’t appear until child is 4 o Most people experience childhood amnesia for events before 3 or 4 - Many developmental features of memory associated with development of temporal lobe and increases in connectivity among cortical areas Frontal lobe development - Frontal deals with language, memory. Also motor and executive function - Prefrontal cortex reaches adult level in teen years - Motor areas mature quickly - Parts of frontal lobes associated with later developing traits take longer - Motor development follows o Cephalocaudal: head is controlled before arms and trunk but arms and trunk are controlled before legs are o Proximodistal: motor skills develop in head, trunk, and arms before hands and fingers - Gross motor skills: involving large muscles for waking, balance, holding up head - Fine-motor skills small muscles for coordination of hands and fingers - Rett syndrome – normal development until 3 or 4
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